1. Field of the Invention
This invention relates to containers having a fluid-tight sealing means for sealing a flexible cover sheet of impermeable material to an impermeable base or other structure formed at least partly of rigid or semi-rigid material and which may be evacuated or pressurised to protect goods on said base.
2. Prior Art
Containers of this type are known, for example, from British Patent No. 1,191,921 and U.S. Pat. Nos. 3,850,214, 3,815,650 and 3,929,178. It is known, see, for example, U.S. Pat. No. 3,850,214, to effect a seal between a flexible envelope and a base of rigid or semi-rigid material by making use of a flexible inflatable tube along the periphery of the sheet material which tube is inserted into a slot or groove in the rigid or semi-rigid material and then inflated into pressure engagement with the walls of the slot or groove. Such a sealing means finds particular application for containers where the base is formed of impermeable material and either air is evacuated from the container so that the flexible sheet collapses downwardly onto goods to hold them firmly on the base or in which a gas, for example dry air, is put into the envelope. The inflatable tube along the periphery of the sheet can be inserted into a groove or slot extending continuously around the base to effect a fluid-tight seal between the flexible sheet material and the base.
When such a container is used for long term storage, it is possible that there may be loss of fluid pressure in the inflated tube so that the tube is pulled out or partly pulled out of the slot or groove. This problem can arise particularly if the container is transportable as stresses may be applied to the cover when the container is moved. For this reason, it has been proposed in the aforementioned U.S. Pat. No. 3,850,214 to provide auxiliary securing means comprising a flap on the cover sheet which is mechanically secured by eyelets engaging hooks on the base of the container. Such a construction prevents the tube being pulled out of the groove or slot but does not necessarily ensure that the seal between the cover sheet and the base remains airtight if pressure is lost in the inflated tube.